FIG. 7 illustrates an exemplary configuration of a virtual library apparatus in a related art. When a data Write request is issued from a host 10 to a hierarchical control server 111 included in the virtual library apparatus 11, the hierarchical control server 111 causes a plurality of logical drives 200 included in a disk array device 112 in the virtual library apparatus 11 to execute the data Write. The logical drives 200 write the data into a logical volume. The hierarchical control server 111 then saves the data written in the abovementioned logical volume in the background, without using the host 10, into a physical tape (medium) loaded into physical drives 123 in a tape library 12 (migration process). Specifically, the hierarchical control server 111 instructs a drive control section 121 included in the tape library 12 to write the data into a physical tape loaded into one of the physical drives 123. Note that a robot 122 is a device to convey and load the physical tape into a physical drive 123.
When an error (for example, a fault) occurs in a physical drive 123 in the background, the hierarchical control server 111 makes the physical drive 123 offline to be disconnected so that the physical drive 123 may not be used by the hierarchical control server. While maintenance operations of the physical drive 123 (head cleaning, faulty part replacement and the like) are performed, the physical drive 123 is prevented from being accessed. After the head cleaning, part replacement operation and the like are performed, the physical drive alone undergoes a diagnostic test offline. After completion of the diagnostic test, the physical drive is made online.
Note that a method for dynamically selecting a plurality of tape drives has been suggested in order to connect a plurality of hosts to a data storage system.
The virtual library apparatus in FIG. 7 makes the physical drive offline to be disconnected and then performs the diagnostic test on the physical drive. Therefore, for example, when a fault occurs on a part between the hierarchical control server 111 and the drive control section 121 in the tape library 12 (such as a cable, driver, and receiver), the physical drive 123 cannot be diagnosed online even if the physical drive 123 is made online and tried to be diagnosed from the host 10 after the aforementioned diagnostic test. Furthermore, if a medium called killer medium which causes a fault in the physical drive exists, a plurality of the physical drives may fail. When many physical drives fail due to the killer medium, it takes time to repair the failed physical drives. Thus, the physical drives must be diagnosed online after the all physical drives involved in the killer medium are exclusively secured. Moreover, it is desired that a physical drive other than the physical drive which is being diagnosed online can be used to execute a general job.